The developmental genetics of Hirschsprung's disease

Genetic regulation of enteric nervous system development in zebrafish

The enteric nervous system (ENS) is a complex series of interconnected neurons and glia that reside within and along the entire length of the gastrointestinal tract. ENS functions are vital to gut homeostasis and digestion, including local control of peristalsis, water balance, and intestinal cell barrier function. How the ENS develops during embryological development is a topic of great concern, as defects in ENS development can result in various diseases, the most common being Hirschsprung disease, in which variable regions of the infant gut lack ENS, with the distal colon most affected. Deciphering how the ENS forms from its progenitor cells, enteric neural crest cells, is an active area of research across various animal models. The vertebrate animal model, zebrafish, has been increasingly leveraged to understand early ENS formation, and over the past 20 years has contributed to our knowledge of the genetic regulation that underlies enteric development. In this review, I summarize our knowledge regarding the genetic regulation of zebrafish enteric neuronal development, and based on the most current literature, present a gene regulatory network inferred to underlie its construction. I also provide perspectives on areas for future zebrafish ENS research.

The transition zone in Hirschsprung's bowel contains abnormal hybrid ganglia with characteristics of extrinsic nerves

The aganglionic bowel in short-segment Hirschsprung's disease is characterized both by the absence of enteric ganglia and the presence of extrinsic thickened nerve bundles (TNBs). The relationship between the TNBs and the loss of enteric ganglia is unknown. Previous studies have described decreasing numbers of ganglia with increasing density of TNBs within the transition zone (TZ) between ganglionic and aganglionic gut, and there is some evidence of spatial contact between them in this region. To determine the cellular interactions involved, we have analysed the expression of perineurial markers of TNBs and enteric ganglionic markers for both neural cells and their ensheathing telocytes across four cranio-caudal segments consisting of most proximal ganglionic to most distal aganglionic from pull-through resected colon. We show that in the TZ, enteric ganglia are abnormal, being surrounded by perineurium cells characteristic of TNBs. Furthermore, short processes of ganglionic neurons extend caudally towards the aganglionic region, where telocytes in the TNB are located between the perineurium and nerve fibres into which they project telopodes. Thus, enteric ganglia within the TZ have abnormal structural characteristics, the cellular relationships of which are shared by the TNBs. These findings will help towards elucidation of the cellular mechanisms involved in the aetiology of Hirschsprung's disease.

Quality of life outcomes in children after surgery for Hirschsprung disease and anorectal malformations: a systematic review and meta-analysis

Background

No systematic review and meta-analysis to date has examined multiple child and parent-reported social and physical quality of life (QoL) in pediatric populations affected by Hirschsprung’s disease (HD) and anorectal malformations (ARM). The objective of this systematic review is to quantitatively summarize the parent-reported and child-reported psychosocial and physical functioning scores of such children.

Methods

Records were sourced from the CENTRAL, EMBASE, and MEDLINE databases. Studies that reported child and parent reported QoL in children with HD and ARM, regardless of surgery intervention, versus children without HD and ARM, were included. The primary outcome was the psychosocial functioning scores, and the secondary outcomes were the presence of postoperative constipation, postoperative obstruction symptoms, fecal incontinence, and enterocolitis. A random effects meta-analysis was used.

Results

Twenty-three studies were included in the systematic review, with 11 studies included in the meta-analysis. Totally, 1678 total pediatric patients with HD and ARM underwent surgery vs 392 healthy controls. Pooled parent-reported standardized mean (SM) scores showed better social functioning after surgery (SM 91.79, 95% CI (80.3 to 103.3), I2=0). The pooled standardized mean difference (SMD) showed evidence for parent-reported incontinence but not for constipation in children with HD and ARM after surgery that had a lower mean QoL score compared with the normal population (SMD −1.24 (-1.79 to –0.69), I2=76% and SMD −0.45, 95% CI (−1.12 to 0.21), I2=75%). The pooled prevalence of child-reported constipation was 22% (95% CI (16% to 28%), I2=0%). The pooled prevalence of parent-reported postoperative obstruction symptoms was 61% (95% CI (41% to 81%), I2=41%).

Conclusion

The results demonstrate better social functioning after surgery, lower QoL scores for incontinence versus controls, and remaining constipation and postoperative obstruction symptoms after surgery in children with HD and ARM.

Aberrant expression of LINC00346 regulates cell migration and proliferation via competitively binding to miRNA-148a-3p/Dnmt1 in Hirschsprung's disease

BACKGROUND

Hirschsprung's disease (HSCR) is a common birth defect caused by dysplasia of neural crest cells in the gut. Long noncoding RNAs (lncRNAs) play an important role in cellular processes, including development and disease. Despite the known engagement of LINC00346 in several human diseases, its biological function in HSCR remains unknown.

METHODS

The relative expression levels of LINC00346, miR-148a-3p and Dnmt1 in HSCR colon tissues were detected by quantitative real-time PCR. Western blot assays were conducted to investigate the Dnmt1 protein expression level. Knockdown of LINC00346 and overexpression of miR-148a-3p in SH-SY5Y and SK-N-BE(2) cell lines was conducted. Cell proliferation and migration were detected by cell counting Kit-8 assays, 5-ethynyl-2'-deoxyuridine assays and transwell assays. Cell apoptosis was verified by flow cytometric analysis. Furthermore, the competing endogenous RNA (ceRNA) activity of LINC00346 on miR-148a-5p was investigated via bioinformatics analysis and luciferase reporter assays.

RESULT

Downregulation of LINC00346 and Dnmt1 was detected in HSCR tissues. Knockdown of LINC00346 and overexpression of miR-148a-3p in SK-N-BE(2) and SH-SY5Y cells inhibited cell migration and proliferation and promoted apoptosis. Moreover, the miR-148a-3p inhibitor rescued the downregulation of Dnmt1 in LINC00346 knockdown cell lines, which was evidence of the ceRNA regulatory mechanism of Dnmt1 by LINC00346.

CONCLUSIONS

LINC00346 was downregulated in HSCR colon tissues and acted as a ceRNA to regulate the expression of Dnmt1 in vitro. Together, these findings indicate that LINC00346 could affect the occurrence of HSCR by participating in the development of enteric neural crest cells.

The Polycomb group gene rnf2 is essential for central and enteric neural system development in zebrafish

The development of central nervous system (CNS) and enteric nervous system (ENS) is under precise and strict control in vertebrates. Whether and how the Polycomb repressive complex 1 (PRC1) is involved in it remain unclear. To investigate the role of PRC1 in the nervous system development, using CRISPR/Cas9 technology, we have generated mutant zebrafish lines for the rnf2 gene which encodes Ring1b, the enzymatic component of the PRC1 complex. We show that rnf2 loss of function leads to abnormal migration and differentiation of neural crest and neural precursor cells. rnf2 mutant embryos exhibit aganglionosis, in which the hindgut is devoid of neurons. In particular, the formation of 5-HT serotonin neurons and myelinating glial cells is defective. Furthermore, ectopic expression of ENS marker genes is observed in forebrain of rnf2 mutant embryos. These findings suggest that the rnf2 gene plays an important role in the migration and differentiation of neural precursor cells, and its absence leads to abnormal development of ENS and CNS in zebrafish.

NR2F1 regulates a Schwann cell precursor-vs-melanocyte cell fate switch in a mouse model of Waardenburg syndrome type IV

Waardenburg syndrome type 4 (WS4) combines abnormal development of neural crest cell (NCC)-derived melanocytes (causing depigmentation and inner ear dysfunction) and enteric nervous system (causing aganglionic megacolon). The full spectrum of WS4 phenotype is present in Spot mice, in which an insertional mutation close to a silencer element leads to NCC-specific upregulation of the transcription factor-coding gene Nr2f1. These mice were previously found to develop aganglionic megacolon because of NR2F1-induced premature differentiation of enteric neural progenitors into enteric glia. Intriguingly, this prior work also showed that inner ear dysfunction in Spot mutants specifically affects balance but not hearing, consistent with the absence of melanocytes in the vestibule only. Here, we report an analysis of the effect of Nr2f1 upregulation on the development of both inner ear and skin melanocytes, also taking in consideration their origin relative to the dorsolateral and ventral NCC migration pathways. In the trunk, we found that NR2F1 overabundance in Spot NCCs forces dorso-laterally migrating melanoblasts to abnormally adopt a Schwann cell precursor (SCP) fate and conversely prevents ventrally migrating SCPs to normally adopt a melanoblast fate. In the head, Nr2f1 upregulation appears not to be uniform, which might explain why SCP-derived melanocytes do colonize the cochlea while non-SCP-derived melanocytes cannot reach the vestibule. Collectively, these data point to a key role for NR2F1 in the control of SCP-vs-melanocyte fate choice and unveil a new pathogenic mechanism for WS4. Moreover, our data argue against the proposed existence of a transit-amplifying compartment of melanocyte precursors in hair follicles.

LncRNA-RMST Functions as a Transcriptional Co-regulator of SOX2 to Regulate miR-1251 in the Progression of Hirschsprung's Disease

Hirschsprung's disease (HSCR) is a congenital disorder characterized by the absence of enteric neural crest cells (ENCCs). LncRNA rhabdomyosarcoma 2-associated transcript (RMST) is essential for the growth and development of neuron. This study aimed to reveal the role of RMST in the pathogenesis of HSCR. The expression level of RMST, miR-1251, SOX2, and AHNAK was evaluated with qRT-PCR or western blot. CCK-8 and transwell assays were applied to detect cell proliferation and migration. CHIP and RIP assays were applied to determine the combination relationship between SOX2 and promoter region of miR-1251 or RMST and SOX2, respectively. Dual-luciferase reporter assay was performed to confirm miR-1251 targeted AHNAK. As results have shown, RMST was downregulated in the aganglionic colon of HSCR patients. The knockdown of RMST attenuated cell proliferation and migration significantly. MiR-1251, the intronic miRNA of RMST, was also low expressed in HSCR, but RMST did not alter the expression of miR-1251 directly. Furthermore, SOX2 was found to regulate the expression of miR-1251 via binding to the promoter region of miR-1251, and RMST strengthened this function by interacting with SOX2. Moreover, AHNAK was the target gene of miR-1251, which was co-regulated by RMST and SOX2. In conclusion, our study demonstrated that RMST functioned as a transcriptional co-regulator of SOX2 to regulate miR-1251 and resulted in the upregulation of AHNAK, leading to the occurrence of HSCR. The novel RMST/SOX2/miR-1251/AHNAK axis provided potential targets for the diagnosis and treatment of HSCR during embryonic stage.

Genetic Background Influences Severity of Colonic Aganglionosis and Response to GDNF Enemas in the Holstein Mouse Model of Hirschsprung Disease

Hirschsprung disease is a congenital malformation where ganglia of the neural crest-derived enteric nervous system are missing over varying lengths of the distal gastrointestinal tract. This complex genetic condition involves both rare and common variants in dozens of genes, many of which have been functionally validated in animal models. Modifier loci present in the genetic background are also believed to influence disease penetrance and severity, but this has not been frequently tested in animal models. Here, we addressed this question using Holstein mice in which aganglionosis is due to excessive deposition of collagen VI around the developing enteric nervous system, thereby allowing us to model trisomy 21-associated Hirschsprung disease. We also asked whether the genetic background might influence the response of Holstein mice to GDNF enemas, which we recently showed to have regenerative properties for the missing enteric nervous system. Compared to Holstein mice in their original FVB/N genetic background, Holstein mice maintained in a C57BL/6N background were found to have a less severe enteric nervous system defect and to be more responsive to GDNF enemas. This change of genetic background had a positive impact on the enteric nervous system only, leaving the neural crest-related pigmentation phenotype of Holstein mice unaffected. Taken together with other similar studies, these results are thus consistent with the notion that the enteric nervous system is more sensitive to genetic background changes than other neural crest derivatives.

From head to tail: regionalization of the neural crest

The neural crest is regionalized along the anteroposterior axis, as demonstrated by foundational lineage-tracing experiments that showed the restricted developmental potential of neural crest cells originating in the head. Here, we explore how recent studies of experimental embryology, genetic circuits and stem cell differentiation have shaped our understanding of the mechanisms that establish axial-specific populations of neural crest cells. Additionally, we evaluate how comparative, anatomical and genomic approaches have informed our current understanding of the evolution of the neural crest and its contribution to the vertebrate body.

Male-biased aganglionic megacolon in the TashT mouse model of Hirschsprung disease involves upregulation of p53 protein activity and Ddx3y gene expression

Hirschsprung disease (HSCR) is a complex genetic disorder of neural crest development resulting in incomplete formation of the enteric nervous system (ENS). This life-threatening neurocristopathy affects 1/5000 live births, with a currently unexplained male-biased ratio. To address this lack of knowledge, we took advantage of the TashT mutant mouse line, which is the only HSCR model to display a robust male bias. Our prior work revealed that the TashT insertional mutation perturbs a Chr.10 silencer-enriched non-coding region, leading to transcriptional dysregulation of hundreds of genes in neural crest-derived ENS progenitors of both sexes. Here, through sex-stratified transcriptome analyses and targeted overexpression in ENS progenitors, we show that male-biased ENS malformation in TashT embryos is not due to upregulation of Sry-the murine ortholog of a candidate gene for the HSCR male bias in humans-but instead involves upregulation of another Y-linked gene, Ddx3y. This discovery might be clinically relevant since we further found that the DDX3Y protein is also expressed in the ENS of a subset of male HSCR patients. Mechanistically, other data including chromosome conformation captured-based assays and CRISPR/Cas9-mediated deletions suggest that Ddx3y upregulation in male TashT ENS progenitors is due to increased transactivation by p53, which appears especially active in these cells yet without triggering apoptosis. Accordingly, in utero treatment of TashT embryos with the p53 inhibitor pifithrin-α decreased Ddx3y expression and abolished the otherwise more severe ENS defect in TashT males. Our data thus highlight novel pathogenic roles for p53 and DDX3Y during ENS formation in mice, a finding that might help to explain the intriguing male bias of HSCR in humans.

Immunohistochemical and ultrastructural analysis of the maturing larval zebrafish enteric nervous system reveals the formation of a neuropil pattern

The gastrointestinal tract is constructed with an intrinsic series of interconnected ganglia that span its entire length, called the enteric nervous system (ENS). The ENS exerts critical local reflex control over many essential gut functions; including peristalsis, water balance, hormone secretions and intestinal barrier homeostasis. ENS ganglia exist as a collection of neurons and glia that are arranged in a series of plexuses throughout the gut: the myenteric plexus and submucosal plexus. While it is known that enteric ganglia are derived from a stem cell population called the neural crest, mechanisms that dictate final neuropil plexus organization remain obscure. Recently, the vertebrate animal, zebrafish, has emerged as a useful model to understand ENS development, however knowledge of its developing myenteric plexus architecture was unknown. Here, we examine myenteric plexus of the maturing zebrafish larval fish histologically over time and find that it consists of a series of tight axon layers and long glial cell processes that wrap the circumference of the gut tube to completely encapsulate it, along all levels of the gut. By late larval stages, complexity of the myenteric plexus increases such that a layer of axons is juxtaposed to concentric layers of glial cells. Ultrastructurally, glial cells contain glial filaments and make intimate contacts with one another in long, thread-like projections. Conserved indicators of vesicular axon profiles are readily abundant throughout the larval plexus neuropil. Together, these data extend our understanding of myenteric plexus architecture in maturing zebrafish, thereby enabling functional studies of its formation in the future.

Downregulation of microRNA-431-5p promotes enteric neural crest cell proliferation via targeting LRSAM1 in Hirschsprung's disease

BACKGROUND

Hirschsprung's disease (HSCR) is characterized by missing of enteric neurons in the terminal areas of the whole gut, which is causally related to poor proliferation of enteric neural crest cells (ENCCs). Our aim is to explore how miR-431-5p interacts with its target gene in regulation of proliferation of ENCCs in HSCR.

METHODS

Mouse model of HSCR was established by Benzalkonium chloride (BAC) treatment. Quantitative Real-time PCR and western blotting were performed to determine the miR-431-5p and the LRSAM1 expression in colon tissues of the HSCR group (n = 8) and the control group (n = 8) and in ENCCs isolated from colon tissues. CCK-8 assay was performed to detect the proliferation of ENCCs of HSCR. ENCCs after transfection with miR-431-5p mimics or miR-431-5p inhibitor. Luciferase reporter assay was conducted to clarify the connections between miR-431-5p and LRSAM1.

RESULTS

Upregulation of miR-431-5p and downregulation of LRSAM1 were found in ENCCs of HSCR. Downregulation of miR-431-5p could promote cell proliferation of ENCCs. LRSAM1 was proved to be the target gene of miR-431-5p by luciferase reporter assay. Moreover, proliferation of ENCCs was increased in the miR-431-5p inhibitor group and was suppressed after knocking down LRSAM1.

CONCLUSION

Downregulation of miR-431-5p promoted proliferation of ENCCs via targeting LRSAM1, which provides an innovative and candidate target for treatment of HSCR.

Gut microbiota-mediated Gene-Environment interaction in the TashT mouse model of Hirschsprung disease

Based on the bilateral relationship between the gut microbiota and formation/function of the enteric nervous system (ENS), we sought to determine whether antibiotics-induced dysbiosis might impact the expressivity of genetically-induced ENS abnormalities. To address this, we took advantage of the TashT mouse model of Hirschsprung disease, in which colonic aganglionosis and hypoganglionosis are both much more severe in males. These defects result into two male-biased colon motility phenotypes: either megacolon that is lethal around weaning age or chronic constipation in adults, the latter being also associated with an increased proportion of nitrergic neurons in the distal ENS. Induction of dysbiosis using a cocktail of broad-spectrum antibiotics specifically impacted the colonic ENS of TashT^Tg/Tg mice in a stage-dependent manner. It further decreased the neuronal density at post-weaning age and differentially modulated the otherwise increased proportion of nitrergic neurons, which appeared normalized around weaning age and further increased at post-weaning age. These changes delayed the development of megacolon around weaning age but led to premature onset of severe constipation later on. Finally, local inhibition of nitric oxide signaling improved motility and prevented death by megacolon. We thus conclude that exposure to antibiotics can negatively influence the expressivity of a genetically-induced enteric neuropathy.

Loss of Tbx3 in murine neural crest reduces enteric glia and causes cleft palate, but does not influence heart development or bowel transit

Transcription factors that coordinate migration, differentiation or proliferation of enteric nervous system (ENS) precursors are not well defined. To identify novel transcriptional regulators of ENS development, we performed microarray analysis at embryonic day (E) 17.5 and identified many genes that were enriched in the ENS compared to other bowel cells. We decided to investigate the T-box transcription factor Tbx3, which is prominently expressed in developing and mature ENS. Haploinsufficiency for TBX3 causes ulnar-mammary syndrome (UMS) in humans, a multi-organ system disorder. TBX3 also regulates several genes known to be important for ENS development. To test the hypothesis that Tbx3 is important for ENS development or function, we inactivated Tbx3 in all neural crest derivatives, including ENS progenitors using Wnt1-Cre and a floxed Tbx3 allele. Tbx3 fl/fl; Wnt1-Cre conditional mutant mice die shortly after birth with cleft palate and difficulty feeding. The ENS of mutants was well-organized with a normal density of enteric neurons and nerve fiber bundles, but small bowel glial cell density was reduced. Despite this, bowel motility appeared normal. Furthermore, although Tbx3 is expressed in cardiac neural crest, Tbx3 fl/fl; Wnt1-Cre mice had structurally normal hearts. Thus, loss of Tbx3 within neural crest has selective effects on Tbx3-expressing neural crest derivatives.

Hirschsprung disease - integrating basic science and clinical medicine to improve outcomes

Hirschsprung disease is defined by the absence of enteric neurons at the end of the bowel. The enteric nervous system (ENS) is the intrinsic nervous system of the bowel and regulates most aspects of bowel function. When the ENS is missing, there are no neurally mediated propulsive motility patterns, and the bowel remains contracted, causing functional obstruction. Symptoms of Hirschsprung disease include constipation, vomiting, abdominal distension and growth failure. Untreated disease usually causes death in childhood because bloodstream bacterial infections occur in the context of bowel inflammation (enterocolitis) or bowel perforation. Current treatment is surgical resection of the bowel to remove or bypass regions where the ENS is missing, but many children have problems after surgery. Although the anatomy of Hirschsprung disease is simple, many clinical features remain enigmatic, and diagnosis and management remain challenging. For example, the age of presentation and the type of symptoms that occur vary dramatically among patients, even though every affected child has missing neurons in the distal bowel at birth. In this Review, basic science discoveries are linked to clinical manifestations of Hirschsprung disease, including partial penetrance, enterocolitis and genetics. Insights into disease mechanisms that might lead to new prevention, diagnostic and treatment strategies are described.

Gli family zinc finger 1 is associated with endothelin receptor type B in Hirschsprung disease

Hirschsprung disease (HSCR) is a newborn colorectal disease characterized by an absence of ganglia in the distal gut. Hedgehog (Hh) and endothelin signaling serve important roles in gastrointestinal tract formation. Alterations in the signaling pathways disrupt the development of enteric neural crest cells (ENCCs). It is not known whether there is any coordination between these pathways in the pathogenesis of HSCR. In the present study, tissue samples from 35 patients with HSCR, including stenotic aganglionosis gut and normal ganglionic gut, were obtained. The expression of Gli family zinc finger 1 (Gli1) and endothelin receptor type B (EDNRB) was determined using reverse transcription-quantitative polymerase chain reaction, immunohistochemistry and western blotting. In addition, the SK-N-SH cell line was used to investigate the association between Hh signaling and the expression of EDNRB. The results revealed aberrant expression of Gli1 in the aganglionic segments, as well as decreased expression of Gli1 in tissues from 7 patients with HSCR exhibited, whereas tissues from 9 patients with HSCR exhibited increased Gli1 expression compared with the expression in the normal tissues. There was a negative association between EDNRB expression and Gli1 expression in the same sample. Knockdown of Gli1 by small interfering RNA and inhibition of Hh signaling by Vismodegib in SK-N-SH cells increased EDNRB expression. By contrast, upregulation of Gli1 expression by plasmids and activation of Hh signaling by Purmorphamine decreased EDNRB expression. Furthermore, premature enteric ganglia were observed in 4 patients with HSCR with decreased Gli1 expression. Thus, the results of the present study suggest that altered Gli1 expression negatively regulates EDNRB expression in patients with HSCR. The increased expression of EDNRB induced by decreased Gli1 expression may represent a novel mechanism in HSCR.

Dysregulation of cotranscriptional alternative splicing underlies CHARGE syndrome

CHARGE syndrome-which stands for coloboma of the eye, heart defects, atresia of choanae, retardation of growth/development, genital abnormalities, and ear anomalies-is a severe developmental disorder with wide phenotypic variability, caused mainly by mutations in CHD7 (chromodomain helicase DNA-binding protein 7), known to encode a chromatin remodeler. The genetic lesions responsible for CHD7 mutation-negative cases are unknown, at least in part because the pathogenic mechanisms underlying CHARGE syndrome remain poorly defined. Here, we report the characterization of a mouse model for CHD7 mutation-negative cases of CHARGE syndrome generated by insertional mutagenesis of Fam172a (family with sequence similarity 172, member A). We show that Fam172a plays a key role in the regulation of cotranscriptional alternative splicing, notably by interacting with Ago2 (Argonaute-2) and Chd7. Validation studies in a human cohort allow us to propose that dysregulation of cotranscriptional alternative splicing is a unifying pathogenic mechanism for both CHD7 mutation-positive and CHD7 mutation-negative cases. We also present evidence that such splicing defects can be corrected in vitro by acute rapamycin treatment.

Retinoic acid temporally orchestrates colonization of the gut by vagal neural crest cells

The enteric nervous system arises from neural crest cells that migrate as chains into and along the primitive gut, subsequently differentiating into enteric neurons and glia. Little is known about the mechanisms governing neural crest migration en route to and along the gut in vivo. Here, we report that Retinoic Acid (RA) temporally controls zebrafish enteric neural crest cell chain migration. In vivo imaging reveals that RA loss severely compromises the integrity and migration of the chain of neural crest cells during the window of time window when they are moving along the foregut. After loss of RA, enteric progenitors accumulate in the foregut and differentiate into enteric neurons, but subsequently undergo apoptosis resulting in a striking neuronal deficit. Moreover, ectopic expression of the transcription factor meis3 and/or the receptor ret, partially rescues enteric neuron colonization after RA attenuation. Collectively, our findings suggest that retinoic acid plays a critical temporal role in promoting enteric neural crest chain migration and neuronal survival upstream of Meis3 and RET in vivo.

Quality of life outcomes in children with Hirschsprung disease

BACKGROUND

Morbidity following repair of Hirschsprung disease (HD) is common. However, quality of life (QoL) results focused on HD children are contradictory. We aimed to measure QoL outcomes in HD children using validated questionnaires.

METHODS

Patients with HD, managed at a large tertiary pediatric institution between 2004 and 2013, were identified. Parents completed validated questionnaires. Results were compared with published healthy population controls. QoL outcomes were measured using Pediatric Quality of Life (PedsQL) and Fecal Incontinence and Constipation Quality of Life (FIC QOL). Functional outcomes were assessed using Baylor Continence Scale, Cleveland Clinic Constipation Scoring System, and Vancouver Dysfunctional Elimination Syndrome Survey.

RESULTS

Parents of 60 HD patients [M:F 49:11; median age 6.4years (2.3-10.9)] were interviewed (59% participation). The majority (47/60, 78%) had rectosigmoid disease. There was significant reduction in psychosocial (social and emotional) QoL compared with healthy children (p=0.03). Psychosocial functioning was affected by increasing age (r=-2.72, p<0.001), fecal incontinence (r=-0.475, p=0.007), constipation (r=-1.58, p=0.006), and dysfunctional elimination (r=-2.94, p=0.004). Fecal incontinence also reduced physical functioning QoL (r=-0.306, p=0.007). Children with HD had significantly higher levels of fecal incontinence (p<0.01).

CONCLUSIONS

We have demonstrated that HD children have significant reductions in psychosocial QoL and functional outcomes.

LEVEL OF EVIDENCE

Prognosis Study - Level II (Prospective cohort study).

Down-regulation of fibronectin and the correlated expression of neuroligin in hirschsprung disease

AIM

The goal of this study was to investigate the expression of fibronectin (FN) and the correlated abundance of neuroligins (NLs) in the enteric nervous system (ENS) and to find a novel diagnostic marker in the serum of Hirschsprung disease (HSCR) patients.

METHODS

The expression levels of FN, neuroligin-1 and neuroligin-2 were detected in 114 children with or without HSCR. The expression and localization of the NLs and FN were assessed morphologically by immunohistochemical staining. Western blot analysis and real-time fluorescence quantitative PCR (qPCR) were performed to examine the correlated expression of the NLs and FN in aganglionic, transitional, and normal ganglionic colon tissues. An enzyme-linked immunosorbent assay (ELISA) was performed to evaluate and compare serum FN levels between HSCR and non-HSCRand between long-type HSCR and short-type HSCR.

RESULTS

These studies showed that both neuroligin-1 and neuroligin-2 were expressed at low levels in aganglionic segments and at intermediate levels in transitional segments compared to their high level of expression in normal tissue. In contrast, FN expression was negatively correlated, with expression in these three samples transitioning from highest to lowest. The serum FN level was higher in HSCR than in non-HSCR, but no significant difference between short-type HSCR and long-type HSCR was observed.

CONCLUSION

FN affects the expression of both neuroligin-1 and neuroligin-2 in HSCR, which may lead to the hypoplasia of ganglion cells in the ENS. This correlation may play a key role in the pathogenesis, diagnosis, or classification of HSCR.

Downregulation of lncRNA MEG3 and miR-770-5p inhibit cell migration and proliferation in Hirschsprung's disease

The long noncoding RNA (lncRNA) MEG3 is involved in various biological processes including cell migration and cell proliferation. In present study, it was found that MEG3 and the intronic miR-770-5p were decreased in samples from HSCR patients. Besides, knockdown of MEG3 and miR-770-5p suppressed cell migration and proliferation, while cell cycle and apoptosis were not affected in human 293T and SH-SY5Y cells. SRGAP1 mRNA and protein upregulation was inversely correlated with miR-770-5p expression in tissue samples and cell lines, which was confirmed to be a target gene of miR-770-5p by dual-luciferase reporter assay. Moreover, silencing of SRGAP1 rescued the inhibition of cell migration and proliferation induced by MEG3 siRNA and miR-770-5p inhibition. The present study elucidates a novel mechanism of the development of HSCR and shows that the MEG3/miR-770-5p/SRGAP1 pathway plays a vital role in the pathogenesis of HSCR.

Maternal use of selective serotonin reuptake inhibitors during pregnancy is associated with Hirschsprung's disease in newborns - a nationwide cohort study

BACKGROUND

Hirschsprung's disease is a rare condition caused by congenital malformation of the gastrointestinal tract affecting 1:5000 children. Not much is known about risk factors for development of Hirschsprung's disease. Two clinical cases of hirschsprung's disease led to an investigation of the association between maternal use of selective serotonin reuptake inhibitors (SSRIs) during pregnancy and development of Hirschsprung's Disease in the newborn child. The study examined a nationwide, unselected cohort of children born in Denmark from 1 January 1996 until 12 March 2016 (n = 1,256,317). We applied multivariate models to register-based data to estimate the odds ratio of Hirschsprung's disease, adjusting for possible confounders. The studied exposure period for SSRIs were 30 days prior to conception to the end of the first trimester.

RESULTS

In the main exposed cohort the prevalence of Hirschsprung's disease was 16/19.807 (0.08%) compared to 584/1.236.510 (0.05%) in the unexposed cohort. In women who redeemed a minimum of one prescription of selective serotonin reuptake inhibitors, the adjusted odds ratio for development of Hirschsprung's disease was 1.76 (95%CI: 1.07-2.92). In women who redeemed a minimum of two prescriptions, the adjusted odds ratio for Hirschsprung's disease was 2.34 (95% CI: 1.21-4.55).

CONCLUSIONS

Our data suggest that early maternal use of selective serotonin reuptake inhibitors is significantly associated with the development of Hirschsprung's disease in the newborn child. Treatment of depression during pregnancy always has to be weighed against the risks posed by untreated maternal depression. Our results have to be confirmed in other studies.

Defining the transcriptomic landscape of the developing enteric nervous system and its cellular environment

BACKGROUND

Motility and the coordination of moving food through the gastrointestinal tract rely on a complex network of neurons known as the enteric nervous system (ENS). Despite its critical function, many of the molecular mechanisms that direct the development of the ENS and the elaboration of neural network connections remain unknown. The goal of this study was to transcriptionally identify molecular pathways and candidate genes that drive specification, differentiation and the neural circuitry of specific neural progenitors, the phox2b expressing ENS cell lineage, during normal enteric nervous system development. Because ENS development is tightly linked to its environment, the transcriptional landscape of the cellular environment of the intestine was also analyzed.

RESULTS

Thousands of zebrafish intestines were manually dissected from a transgenic line expressing green fluorescent protein under the phox2b regulatory elements [Tg(phox2b:EGFP) ^w37 ]. Fluorescence-activated cell sorting was used to separate GFP-positive phox2b expressing ENS progenitor and derivatives from GFP-negative intestinal cells. RNA-seq was performed to obtain accurate, reproducible transcriptional profiles and the unbiased detection of low level transcripts. Analysis revealed genes and pathways that may function in ENS cell determination, genes that may be identifiers of different ENS subtypes, and genes that define the non-neural cellular microenvironment of the ENS. Differential expression analysis between the two cell populations revealed the expected neuronal nature of the phox2b expressing lineage including the enrichment for genes required for neurogenesis and synaptogenesis, and identified many novel genes not previously associated with ENS development. Pathway analysis pointed to a high level of G-protein coupled pathway activation, and identified novel roles for candidate pathways such as the Nogo/Reticulon axon guidance pathway in ENS development.

CONCLUSION

We report the comprehensive gene expression profiles of a lineage-specific population of enteric progenitors, their derivatives, and their microenvironment during normal enteric nervous system development. Our results confirm previously implicated genes and pathways required for ENS development, and also identify scores of novel candidate genes and pathways. Thus, our dataset suggests various potential mechanisms that drive ENS development facilitating characterization and discovery of novel therapeutic strategies to improve gastrointestinal disorders.

Toward a better understanding of enteric gliogenesis

Most of gastrointestinal functions are controlled by the enteric nervous system (ENS), which contains a vast diversity of neurons and glial cells. In accordance with its key role, defective ENS formation is the cause of several diseases that affect quality of life and can even be life-threatening. Treatment of these diseases would greatly benefit from a better understanding of the molecular mechanisms underlying ENS formation. In this regard, although several important discoveries have been made over the years, how the full spectrum of enteric neuronal and glial cell subtypes is generated from neural crest cells during development still remains enigmatic. Because they also have stem cell properties, such knowledge would be especially important for the enteric glial cell lineage. In a recent study, we identified the NR2F1 transcription factor as a new key regulator of enteric gliogenesis. Here we discuss our recent findings and briefly review what is already known about the mechanisms and signaling pathways involved in enteric gliogenesis, with an emphasis on Hedgehog and Notch signaling.

Male-specific colon motility dysfunction in the TashT mouse line

BACKGROUND

In Hirschsprung disease (HSCR), the absence of myenteric neural ganglia in the distal bowel prevents motility and thereby causes functional intestinal obstruction. Although surgical resection of the aganglionic segment allows HSCR children to survive this condition, a number of patients still suffer from impaired motility despite having myenteric ganglia in their postoperative distal bowel. Such phenomenon is also observed in patients suffering from other enteric neuropathies and, in both cases, colonic dysmotility is believed to result from abnormalities of myenteric ganglia and/or associated interstitial cells of Cajal (ICC). To better understand this, we used a recently described HSCR mouse model called TashT.

METHODS

Intestinal motility parameters were assessed and correlated with extent of aganglionosis and with neuronal density in ganglionated regions. The neural composition of the myenteric plexus and the status of ICC networks was also evaluated using immunofluorescence.

KEY RESULTS

TashT(Tg/Tg) mice display a strong male bias in the severity of both colonic aganglionosis and hypoganglionosis, which are associated with male-specific reduced colonic motility. TashT(Tg/Tg) male mice also exhibit a specific increase in nNos(+) neurons that is restricted to the most distal ganglionated regions. In contrast, Calretinin(+) myenteric neurons, Sox10(+) myenteric glial cells, and cKit(+) ICC are not affected in TashT(Tg/Tg) mice.

CONCLUSIONS AND INFERENCES

Male-specific impairment of colonic motility in TashT(Tg/Tg) mice is associated with both severe hypoganglionosis and myenteric neuronal imbalance. Considering these parameters in the clinic might be important for the management of postoperative HSCR patients.

Enteric nervous system stem cells associated with thickened extrinsic fibers in short segment aganglionic Hirschsprung's disease gut are absent in the total colonic and intestinal variants of disease

BACKGROUND/PURPOSE

Despite current treatments patients with Hirschsprung's disease (HSCR) suffer significant long-term morbidity. Therefore, there is increasing interest in adjunctive therapies, such as using enteric nervous system stem cells (ENSSC), isolated from typical aganglionic bowel. The source of these cells is unclear however it is hypothesized that they are present in the thickened nerve trunks in aganglionic short and long segment HSCR gut. These cells should therefore be absent in total colonic and pan intestinal HSCR where these thickened fibers are absent.

METHODS

Cells were isolated from samples of short segment HSCR gut (n=18) and total colonic and total intestinal HSCR gut (n=2). Acetylcholinesterase histochemistry confirmed the presence/absence of thickened nerve trunks. P75 immunofluorescence highlighted ENSSC at isolation and after 10days in culture in both groups.

RESULTS

ENSSC were not isolated or cultured from total colonic and total intestinal HSCR gut where thickened nerve trunks were absent. In contrast 10.0% (+/-1.9 SEM) of cells from short segment HSCR gut were ENSSC at isolation rising to 22.7% (+/-2.9 SEM) after 10days in culture.

CONCLUSIONS

These results associate ENSCC with thickened nerve trunks and also suggest that the aganglionic bowel segment in total colonic and intestinal HSCR cannot be used as a source of ENSCC for adjunctive therapy.

Upregulation of the Nr2f1-A830082K12Rik gene pair in murine neural crest cells results in a complex phenotype reminiscent of Waardenburg syndrome type 4

Waardenburg syndrome is a neurocristopathy characterized by a combination of skin and hair depigmentation, and inner ear defects. In the type 4 form, these defects show comorbidity with Hirschsprung disease, a disorder marked by an absence of neural ganglia in the distal colon, triggering functional intestinal obstruction. Here, we report that the Spot mouse line - obtained through an insertional mutagenesis screen for genes involved in neural crest cell (NCC) development - is a model for Waardenburg syndrome type 4. We found that the Spot insertional mutation causes overexpression of an overlapping gene pair composed of the transcription-factor-encoding Nr2f1 and the antisense long non-coding RNA A830082K12Rik in NCCs through a mechanism involving relief of repression of these genes. Consistent with the previously described role of Nr2f1 in promoting gliogenesis in the central nervous system, we further found that NCC-derived progenitors of the enteric nervous system fail to fully colonize Spot embryonic guts owing to their premature differentiation in glial cells. Taken together, our data thus identify silencer elements of the Nr2f1-A830082K12Rik gene pair as new candidate loci for Waardenburg syndrome type 4.

Mouse models of Hirschsprung disease and other developmental disorders of the enteric nervous system: Old and new players

Hirschsprung disease (HSCR, intestinal aganglionosis) is a multigenic disorder with variable penetrance and severity that has a general population incidence of 1/5000 live births. Studies using animal models have contributed to our understanding of the developmental origins of HSCR and the genetic complexity of this disease. This review summarizes recent progress in understanding control of enteric nervous system (ENS) development through analyses in mouse models. An overview of signaling pathways that have long been known to control the migration, proliferation and differentiation of enteric neural progenitors into and along the developing gut is provided as a framework for the latest information on factors that influence enteric ganglia formation and maintenance. Newly identified genes and additional factors beyond discrete genes that contribute to ENS pathology including regulatory sequences, miRNAs and environmental factors are also introduced. Finally, because HSCR has become a paradigm for complex oligogenic diseases with non-Mendelian inheritance, the importance of gene interactions, modifier genes, and initial studies on genetic background effects are outlined.

White paper on guidelines concerning enteric nervous system stem cell therapy for enteric neuropathies

Over the last 20 years, there has been increasing focus on the development of novel stem cell based therapies for the treatment of disorders and diseases affecting the enteric nervous system (ENS) of the gastrointestinal tract (so-called enteric neuropathies). Here, the idea is that ENS progenitor/stem cells could be transplanted into the gut wall to replace the damaged or absent neurons and glia of the ENS. This White Paper sets out experts' views on the commonly used methods and approaches to identify, isolate, purify, expand and optimize ENS stem cells, transplant them into the bowel, and assess transplant success, including restoration of gut function. We also highlight obstacles that must be overcome in order to progress from successful preclinical studies in animal models to ENS stem cell therapies in the clinic.

Pigmentation-based insertional mutagenesis is a simple and potent screening approach for identifying neurocristopathy-associated genes in mice

Neurocristopathies form a specific group of rare genetic diseases in which a defect in neural crest cell development is causal. Because of the large number of neural crest cell derivatives, distinct structures/cell types (isolated or in combination) are affected in each neurocristopathy. The most important issues in this research field is that the underlying genetic cause and associated pathogenic mechanism of most cases of neurocristopathy are poorly understood. This article describes how a relatively simple insertional mutagenesis approach in the mouse has proved useful for identifying new candidate genes and pathogenic mechanisms for diverse neurocristopathies.

A novel subset of enteric neurons revealed by ptf1a:GFP in the developing zebrafish enteric nervous system

The enteric nervous system, the largest division of the peripheral nervous system, is derived from vagal neural crest cells that invade and populate the entire length of the gut to form diverse neuronal subtypes. Here, we identify a novel population of neurons within the enteric nervous system of zebrafish larvae that express the transgenic marker ptf1a:GFP within the midgut. Genetic lineage analysis reveals that enteric ptf1a:GFP(+) cells are derived from the neural crest and that most ptf1a:GFP(+) neurons express the neurotransmitter 5HT, demonstrating that they are serotonergic. This transgenic line, Tg(ptf1a:GFP), provides a novel neuronal marker for a subpopulation of neurons within the enteric nervous system, and highlights the possibility that Ptf1a may act as an important transcription factor for enteric neuron development.

A collagen VI-dependent pathogenic mechanism for Hirschsprung's disease

Hirschsprung's disease (HSCR) is a severe congenital anomaly of the enteric nervous system (ENS) characterized by functional intestinal obstruction due to a lack of intrinsic innervation in the distal bowel. Distal innervation deficiency results from incomplete colonization of the bowel by enteric neural crest cells (eNCCs), the ENS precursors. Here, we report the generation of a mouse model for HSCR--named Holstein--that contains an untargeted transgenic insertion upstream of the collagen-6α4 (Col6a4) gene. This insertion induces eNCC-specific upregulation of Col6a4 expression that increases total collagen VI protein levels in the extracellular matrix (ECM) surrounding both the developing and the postnatal ENS. Increased collagen VI levels during development mainly result in slower migration of eNCCs. This appears to be due to the fact that collagen VI is a poor substratum for supporting eNCC migration and can even interfere with the migration-promoting effects of fibronectin. Importantly, for a majority of patients in a HSCR cohort, the myenteric ganglia from the ganglionated region are also specifically surrounded by abundant collagen VI microfibrils, an outcome accentuated by Down syndrome. Collectively, our data thus unveil a clinically relevant pathogenic mechanism for HSCR that involves cell-autonomous changes in ECM composition surrounding eNCCs. Moreover, as COL6A1 and COL6A2 are on human Chr.21q, this mechanism is highly relevant to the predisposition of patients with Down syndrome to HSCR.

Meis3 is required for neural crest invasion of the gut during zebrafish enteric nervous system development

Loss of Meis3 leads to defects in enteric neural crest cell migration, number, and proliferation during colonization of the gut. This leads to colonic aganglionosis, in which the hindgut is devoid of neurons, identifying it as a novel candidate factor in the etiology of Hirschsprung’s disease during enteric nervous system development.

During development, vagal neural crest cells fated to contribute to the enteric nervous system migrate ventrally away from the neural tube toward and along the primitive gut. The molecular mechanisms that regulate their early migration en route to and entry into the gut remain elusive. Here we show that the transcription factor meis3 is expressed along vagal neural crest pathways. Meis3 loss of function results in a reduction in migration efficiency, cell number, and the mitotic activity of neural crest cells in the vicinity of the gut but has no effect on neural crest or gut specification. Later, during enteric nervous system differentiation, Meis3-depleted embryos exhibit colonic aganglionosis, a disorder in which the hindgut is devoid of neurons. Accordingly, the expression of Shh pathway components, previously shown to have a role in the etiology of Hirschsprung’s disease, was misregulated within the gut after loss of Meis3. Taken together, these findings support a model in which Meis3 is required for neural crest proliferation, migration into, and colonization of the gut such that its loss leads to severe defects in enteric nervous system development.

Submandibular parasympathetic gangliogenesis requires sprouty-dependent Wnt signals from epithelial progenitors

Parasympathetic innervation is critical for submandibular gland (SMG) development and regeneration. Parasympathetic ganglia (PSG) are derived from Schwann cell precursors that migrate along nerves, differentiate into neurons, and coalesce within their target tissue to form ganglia. However, signals that initiate gangliogenesis after the precursors differentiate into neurons are unknown. We found that deleting negative regulators of FGF signaling, Sprouty1 and Sprouty2 (Spry1/2DKO), resulted in a striking loss of gangliogenesis, innervation, and keratin 5-positive (K5+) epithelial progenitors in the SMG. Here we identify Wnts produced by K5+ progenitors in the SMG as key mediators of gangliogenesis. Wnt signaling increases survival and proliferation of PSG neurons, and inhibiting Wnt signaling disrupts gangliogenesis and organ innervation. Activating Wnt signaling and reducing FGF gene dosage rescues gangliogenesis and innervation in both the Spry1/2DKO SMG and pancreas. Thus, K5+ progenitors produce Wnt signals to establish the PSG-epithelial communication required for organ innervation and progenitor cell maintenance.

Male-biased aganglionic megacolon in the TashT mouse line due to perturbation of silencer elements in a large gene desert of chromosome 10

Neural crest cells (NCC) are a transient migratory cell population that generates diverse cell types such as neurons and glia of the enteric nervous system (ENS). Via an insertional mutation screen for loci affecting NCC development in mice, we identified one line—named TashT—that displays a partially penetrant aganglionic megacolon phenotype in a strong male-biased manner. Interestingly, this phenotype is highly reminiscent of human Hirschsprung’s disease, a neurocristopathy with a still unexplained male sex bias. In contrast to the megacolon phenotype, colonic aganglionosis is almost fully penetrant in homozygous TashT animals. The sex bias in megacolon expressivity can be explained by the fact that the male ENS ends, on average, around a “tipping point” of minimal colonic ganglionosis while the female ENS ends, on average, just beyond it. Detailed analysis of embryonic intestines revealed that aganglionosis in homozygous TashT animals is due to slower migration of enteric NCC. The TashT insertional mutation is localized in a gene desert containing multiple highly conserved elements that exhibit repressive activity in reporter assays. RNAseq analyses and 3C assays revealed that the TashT insertion results, at least in part, in NCC-specific relief of repression of the uncharacterized gene Fam162b; an outcome independently confirmed via transient transgenesis. The transcriptional signature of enteric NCC from homozygous TashT embryos is also characterized by the deregulation of genes encoding members of the most important signaling pathways for ENS formation—Gdnf/Ret and Edn3/Ednrb—and, intriguingly, the downregulation of specific subsets of X-linked genes. In conclusion, this study not only allowed the identification of Fam162b coding and regulatory sequences as novel candidate loci for Hirschsprung’s disease but also provides important new insights into its male sex bias.

Hirschsprung’s disease (also known as aganglionic megacolon) is a severe congenital defect of the enteric nervous system (ENS) resulting in complete failure to pass stools. It is characterized by the absence of neural ganglia (aganglionosis) in the distal gut due to incomplete colonization of the embryonic intestines by neural crest cells (NCC), the ENS precursors. Hirschsprung’s disease has an incidence of 1 in 5000 newborns and a 4:1 male sex bias. Although many genes have been associated with this complex genetic disease, most of its heritability as well as its male sex bias remain unexplained. Here, we describe an insertional mutant mouse line (“TashT”) in which virtually all homozygotes display colonic aganglionosis due to defective migration of enteric NCC, but in which only a subset of homozygotes develops megacolon. Surprisingly, this group is almost exclusively male. The TashT ENS defect stems, at least in part, from the disruption of long-range interactions between evolutionarily conserved elements with silencer activity and Fam162b, resulting in NCC-specific upregulation of this uncharacterized protein coding gene. Global analysis of gene expression further revealed that several hundreds of genes are significantly deregulated in TashT enteric NCC. Interestingly, this dataset includes multiple X-linked candidate genes potentially underlying the male sex bias. Taken together, our data pave the way for a clearer understanding of the intriguing male sex bias of Hirschsprung’s disease.

Beta-actin is required for proper mouse neural crest ontogeny

The mouse genome consists of six functional actin genes of which the expression patterns are temporally and spatially regulated during development and in the adult organism. Deletion of beta-actin in mouse is lethal during embryonic development, although there is compensatory expression of other actin isoforms. This suggests different isoform specific functions and, more in particular, an important function for beta-actin during early mammalian development. We here report a role for beta-actin during neural crest ontogeny. Although beta-actin null neural crest cells show expression of neural crest markers, less cells delaminate and their migration arrests shortly after. These phenotypes were associated with elevated apoptosis levels in neural crest cells, whereas proliferation levels were unchanged. Specifically the pre-migratory neural crest cells displayed higher levels of apoptosis, suggesting increased apoptosis in the neural tube accounts for the decreased amount of migrating neural crest cells seen in the beta-actin null embryos. These cells additionally displayed a lack of membrane bound N-cadherin and dramatic decrease in cadherin-11 expression which was more pronounced in the pre-migratory neural crest population, potentially indicating linkage between the cadherin-11 expression and apoptosis. By inhibiting ROCK ex vivo, the knockout neural crest cells regained migratory capacity and cadherin-11 expression was upregulated. We conclude that the presence of beta-actin is vital for survival, specifically of pre-migratory neural crest cells, their proper emigration from the neural tube and their subsequent migration. Furthermore, the absence of beta-actin affects cadherin-11 and N-cadherin function, which could partly be alleviated by ROCK inhibition, situating the Rho-ROCK signaling in a feedback loop with cadherin-11.

A quantitative cell migration assay for murine enteric neural progenitors

Neural crest cells (NCC) are a transient and multipotent cell population that originates from the dorsal neural tube and migrates extensively throughout the developing vertebrate embryo. In addition to providing peripheral glia and neurons, NCC generate melanocytes as well as most of the cranio-facial skeleton. NCC migration and differentiation is controlled by a combination of their axial origin along the neural tube and their exposure to regionally distinct extracellular cues. Such contribution of extracellular ligands is especially evident during the formation of the enteric nervous system (ENS), a complex interconnected network of neural ganglia that locally controls (among other things) gut muscle movement and intestinal motility. Most of the ENS is derived from a small initial pool of NCC that undertake a long journey in order to colonize - in a rostral to caudal fashion - the entire length of the prospective gut. Among several signaling pathways known to influence enteric NCC colonization, GDNF/RET signaling is recognized as the most important. Indeed, spatiotemporally controlled secretion of the RET ligand GDNF by the gut mesenchyme is chiefly responsible for the attraction and guidance of RET-expressing enteric NCC to and within the embryonic gut. Here, we describe an ex vivo cell migration assay, making use of a transgenic mouse line possessing fluorescently labeled NCC, which allows precise quantification of enteric NCC migration potential in the presence of various growth factors, including GDNF.

Enteric nervous system development: migration, differentiation, and disease

The enteric nervous system (ENS) provides the intrinsic innervation of the bowel and is the most neurochemically diverse branch of the peripheral nervous system, consisting of two layers of ganglia and fibers encircling the gastrointestinal tract. The ENS is vital for life and is capable of autonomous regulation of motility and secretion. Developmental studies in model organisms and genetic studies of the most common congenital disease of the ENS, Hirschsprung disease, have provided a detailed understanding of ENS development. The ENS originates in the neural crest, mostly from the vagal levels of the neuraxis, which invades, proliferates, and migrates within the intestinal wall until the entire bowel is colonized with enteric neural crest-derived cells (ENCDCs). After initial migration, the ENS develops further by responding to guidance factors and morphogens that pattern the bowel concentrically, differentiating into glia and neuronal subtypes and wiring together to form a functional nervous system. Molecules controlling this process, including glial cell line-derived neurotrophic factor and its receptor RET, endothelin (ET)-3 and its receptor endothelin receptor type B, and transcription factors such as SOX10 and PHOX2B, are required for ENS development in humans. Important areas of active investigation include mechanisms that guide ENCDC migration, the role and signals downstream of endothelin receptor type B, and control of differentiation, neurochemical coding, and axonal targeting. Recent work also focuses on disease treatment by exploring the natural role of ENS stem cells and investigating potential therapeutic uses. Disease prevention may also be possible by modifying the fetal microenvironment to reduce the penetrance of Hirschsprung disease-causing mutations.